Secretory IgA as a measure of immunocompetence

The field of psychoimmunology has rapidly expanded in recent years and various parameters of the immune system have been examined in relation to psychological factors. The secretory immune system is one of the more interesting aspects of the entire immune system because it protects mucosal membranes from invading organisms. Stress-produced changes in secretory immunoglobulin A (s-IgA) as measured by radial immunodiffusion assays have been reported in several studies. We present three reasons why total s-IgA protein, the measure derived from radial immunodiffusion assays, may not be a reasonable measure of immune system functioning, and we suggest an alternative method for examining secretory IgA that focuses on s-IgA antibody response to a novel antigen.     

Components of pollination effectiveness in Psychotria suerrensis,a tropical distylous shrub

In this paper I report components of effectiveness for pollinators of a tropical distylous shrub, Psychotria suerrensis (Rubiaceae), which is visited by a variety of bees, wasps, and butterflies, and by two species of hummingbirds. In the field, I measured the following components of effectiveness: frequency of visits, evenness of visits across plants, and diurnal pattern of visits. I also used flight-cage experiments to compare pollentransfer abilities of euglossine bees and heliconiid butterflies. Euglossine bees visited more frequently, visited earlier in the day, and visited a higher proportion of plants in the population than did other taxa. In flight cage experiments, bees and butterflies transferred similar amounts of pollen overall, but bees transferred significantly more inter-morph (compatible) pollen. For each component measured, euglossine bees appeared to be the most effective pollinators.     

Mass Coral Reef Bleaching: A Recent Outcome of Increased El Niño Activity?

Coral reefs are generally considered to be the most biologically productive of all marine ecosystems, but in recent times these vulnerable aquatic resources have been subject to unusual degradation. The general decline in reefs has been greatly accelerated by mass bleaching in which corals whiten en masse and often fail to recover. Empirical evidence indicates a coral reef bleaching cycle in which major bleaching episodes are synchronized with El Niño events that occur every 3–4 years on average. By heating vast areas of the Pacific Ocean, and affecting the Indian and Atlantic Oceans as well, El Niño causes widespread damage to reefs largely because corals are very sensitive to temperature changes. However, mass bleaching events were rarely observed before the 1970s and their abrupt appearance two decades ago remains an enigma. Here we propose a new explanation for the sudden occurrence of mass bleaching and show that it may be a response to the relative increase in El Niño experienced over the last two decades.     

Genetic research with nonhuman primates: serving the needs of mankind Symposium summary and future prospects

The wide array of papers delivered at this symposium, ranging from population genetics to molecular genetics, is convincing evidence that genetic research with nonhuman primates is in full bloom. In fact, progress has been quite remarkable considering that a significant number of pedigreed colonies of nonhuman primates have been available for less than 25 years, which is hardly enough time to raise 3 generations of chimpanzees, 5 generations of baboons or 6 generations of rhesus monkeys. Were it not for these pedigreed colonies, we would not have been privileged to have this assemblage of papers on behavior, social structure, predisposition to disease and management of breeding colonies. It is indeed exciting that preliminary evidence has been obtained for major genes that play a role in susceptibility to dyslipoproteinemias in baboons, and that monoclonal antibodies and DNA markers are helping us to understand cholesterol metabolism. And thanks to computers, we can now rank animals in a colony in terms of their useful genotypes as well as their productivity. One can not help but be impressed with the commonality of humans and nonhuman primates at the structural and functional levels. For example, the major histocompatibility systems and the maternal-fetal relationships are very similar. We heard that this similarity is even more striking at the chromosomal, biochemical and DNA levels. A provocative question yet to be answered is, “what accounts for the obvious differences between humans and nonhuman primates in view of these incredible similarities?” In light of these advances, this symposium was at the cutting edge of primate genetics and the papers published in this issue of Genetica are certain to be hallmarks in the literature.     

Isolation and reconstitution of the dicyclohexylcarbodiimide-sensitive proton pore of the clathrin-coated vesicle proton translocating complex

The clathrin-coated vesicle proton translocating complex is composed of a maximum of eight polypeptides. The function of the components of this system have not been defined. Proton pumping catalyzed by the reconstituted, 200-fold purified proton translocating complex of clathrin-coated vesicles is inhibited 50% at a dicyclohexylcarbodiimide (DCCD)/protein ratio of 0.66 mumol of DCCD/mg of protein. At an identical DCCD/protein ratio, the 17-kDa component of the proton pump is labeled by [14C]DCCD. Through toluene extraction, the 17-kDa subunit has been isolated from the holoenzyme. The 17-kDa polypeptide diminished proteoliposome acidification when coreconstituted with either bacteriorhodopsin or the intact clathrin-coated vesicle proton translocating ATPase. In both instances, treatment of the 17-kDa polypeptide with DCCD restored proteoliposome acidification. Moreover, the proton-conducting activity of the 17-kDa polypeptide is abolished by trypsin digestion. These results demonstrate that the 17-kDa polypeptide present in the isolated proton ATPase of clathrin-coated vesicles is a subunit which functions as a transmembranous proton pore.     

Hepatic metabolism and secretion of a cholesterol-enriched lipoprotein fraction

A potentially important source of cholesterol secreted in bile is cholesterol-rich lipoproteins. However, the fate of the cholesterol carried in these lipoproteins after hepatic uptake has not been investigated. We harvested an apoE- and cholesterol-rich lipoprotein fraction (d 1.02-1.06 g/ml) from hypercholesterolemic rats and examined the acute effects of these lipoproteins on hepatic cholesterol metabolism, very low density lipoprotein (VLDL) secretion, and biliary lipid secretion. Administration of a lipoprotein bolus (20 mg of cholesterol) to rats resulted in a significant decrease in 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and a significant increase in acyl-coenzyme A:cholesterol acyltransferase activity over controls at 1 hr. Hepatic cholesteryl ester content increased 400% with no change in hepatic free cholesterol content or biliary cholesterol secretion. These cholesterol-rich lipoproteins delivered in the isolated perfused liver effected a fivefold increase in hepatic VLDL secretion with no change in composition. Therefore, cholesterol-rich lipoproteins do not acutely alter biliary cholesterol secretion. Rather, the majority of the cholesterol delivered to the liver in these lipoproteins is either esterified and stored as cholesteryl ester or resecreted as free and esterified cholesterol in hepatic VLDL.